1. Field of The Invention
This invention relates to an organopolysiloxane composition which is adapted for use as a core material for plastic optical fibers. The invention also relates to a plastic optical fiber comprising a core made of a cured product of the composition.
2. Description of the Prior Art
As is well known in the art, optical fibers include, aside from glass optical fibers wherein quartz glass or multicomponent glasses are, respectively, used as a core component and also as a clad component, plastic optical fibers wherein both core and clad components are, respectively, made of plastics. The plastic optical fiber is disadvantageous in that it is greater in transmission loss than glass optical fibers, but with the advantage in that the plastic optical fiber is more likely to make a greater numerical aperture and is easier in handling and more inexpensive than glass optical fibers.
In usual practice, the plastic optical fiber is constituted of a core made of an organic polymer whose optical transparency is good and a clad made of an organic polymer whose refractive index is smaller than that of the core and which has a good transparency. Examples of the organic polymers which are suitable for use as a core material having good optical transmission include polymethyl methacrylate, polystyrene and the like. In recent years, organopolysiloxane elastomers have been proposed as a core material, for example, in Japanese Laid-open Patent Application No. 60-43613. The plastic optical fiber using the organopolysiloxane elastomer as the core is better in flexibility and heat resistance than the core component using polymethyl methacrylate.
However, where an organopolysiloxane elastomer is applied as a core material and is employed under moist heat conditions, water vapor is absorbed in the elastomer core although the heat resistance is good. Eventually, when the temperature is changed, the water vapor in the core is condensed, with the disadvantage that the optical transmission of the optical fiber considerably lowers. Thus, there arises the problem that limitation is placed on the use of the optical fiber.
In the field where a heat-resistant, plastic optical fiber is favorably employed, the optical fiber is essentially required to reliably work under high temperature and high humidity conditions. Hence, there is a demand for improving the moistureproofness of the plastic optical fiber.